The comma can signify a pause, but it also has many other grammatical functions. In fact, I would say that most uses of the comma are not actually marking pauses, but since it marks clausal boundaries, it often aligns with pauses. But if we actually used commas to mark all of the places we wanted pauses, sentences would actually look quite strange (and if we paused for every comma, we would sound strange too).
For example if I say "get out" emphatically, with a pause between "get" and "out", would it look right for me to write:
Or, say, something like this:
I, don't know.
Certainly a pause between "I" and "don't" is something people often do in speech, so why is it so strange written that way? Because commas don't actually mark pauses. If anything, we use "..." to mark pauses that aren't clausal boundaries.
In many cases, pausing for commas is clearly unnecessary. For example, when I say "John, Sally, and I went to the park", those commas are required whether or not I pause. When I see "dark, stormy clouds", a comma is required there as well. When I write "it's nice to see you, John", the comma marks the fact that I am addressing John. It doesn't matter if I pause or not.
In the case of your question, you are separating two clauses when you put the comma before "OK". Whether or not you actually pause is irrelevant to the use of the comma, so it should always be there (formally speaking).